Hydrogen generating, oxygen scavenging closure cap

ABSTRACT

The closure cap ( 1 ) is capable of generating molecular hydrogen from a chemical reaction with water, and can be used for closing a container and for scavenging oxygen. The cap ( 1 ) comprises a shell ( 10 ), an active layer ( 11 ) that is capable of chemically reacting with water and generating molecular hydrogen, and a liner ( 12 ) that is permeable to water vapour and to molecular hydrogen; said active layer ( 11 ) has an inner face ( 11   a ), an outer face ( 11   b ) and a circumferential edge ( 11   c ); the shell ( 10 ) comprises an housing and the active layer ( 11 ) is entirely contained in said housing; the outer face ( 11   b ) and the circumferential edge ( 11   c ) of the active layer ( 11 ) are in contact with the shell ( 10 ) and are bonded to the shell ( 10 ); the liner ( 12 ) is closing said housing (H) and is bonded to the shell ( 10 ) on the whole periphery of the active layer ( 11 ) and to the inner face ( 11   a ) of the active layer ( 11 ).

TECHNICAL FIELD

The invention relates to a novel closure cap that is capable ofgenerating molecular hydrogen from a chemical reaction with water, andthat can be used for closing a container and for scavenging oxygen. Thecontainer can be used for storing any oxygen-sensitive substance thatcan be altered by oxygen, and in particular a food substance or abeverage such as for example juice, beer, wine, . . .

PRIOR ART

Aromatic polyester resins, and in particular polyethylene terephthalate(PET), are widely used in the packaging industry for making varioustypes containers for storing any substance, and in particular forstoring food substance or a beverage.

PET has a number of valuable properties for packaging, but lackssufficient gas barrier properties for many applications. In particularbecause of its oxygen permeability, PET alone is not appropriate forpackaging oxygen-sensitive food and beverage products such as beer,fruit juices, some carbonated soft drinks, etc. . . . PET is alsopermeable to carbon dioxide, which in turn leads to a short shelf lifefor carbonated products, such as carbonated soft drinks, stored in PETcontainers.

In order to improve the gas barrier properties of packaging articles, inparticular oxygen and/or carbon dioxide barrier properties, it is nowcommon to use multilayered packaging articles, and in particularmultilayered containers, that include at least one barrier layer. Forexample, in the field of bottle packaging, a typical and commonmultilayered wall structure for a hollow rigid container is athree-layer wall: two internal and external layers made of PET, and oneintermediate gas barrier layer sandwiched between the two PET layers.

A first known type of barrier layer is made of, or comprises, polymersthat have excellent gas-barrier properties, in particular to O₂ and/orCO₂, and is generally referred as “passive barrier layer”. Among thepolymers used for making passive barrier layers, homo- or copolymers ofpolyamides are commonly used. Among these polyamides, the so-called“MXD6” or “MXD6 nylon” (specific polyamide material manufactured byMitsubishi Gas Chemical Company, Japan) is preferably used, i.e. apoly(m-xylyleneadipamide) produced by the polycondensation of a diaminecomponent composed mainly of m-xylylenediamine and a dicarboxylic acidcomponent composed mainly of adipic acid.

A second known type of barrier layer, which has been more recentlydeveloped, is made of, or comprises, polymeric composition that hasoxygen-scavenging properties, and is generally referred as “activebarrier layer”. Generally speaking, an active barrier layer reacts withthe oxygen and “captures” the oxygen when the oxygen penetrates into thelayer. Such active barrier layer is thus progressively “consumed” inuse.

Examples of polymeric compositions used for making active barrier layerare described notably in European patent application EP-A-0 301 719 orin European patent application EP-A-0 507 207. Said polymericcompositions generally comprise an oxidizable polymer and a transitionmetal catalyst. In EP-A-0 301 719, the preferred oxidizable polymers arepolyamides, and especially MXD6. In EP-0 507 207, one preferredoxidizable polymer is polybutadiene. In both cases, preferred transitionmetal catalysts are transition metal salts, an in particular cobaltstearate. Other known metal salts used for making such composition arerhodium, manganese, copper, iron.

With multilayered packaging articles having at least one gas barrierlayer comprising a polyamide (e.g. MXD6) and a polyester (e.g. PET),very good results can be achieved in terms of shelf life of the packagedproducts. More especially when the barrier layer comprises a polyamide(e.g. MXD6), polyester (e.g. PET), and a catalyst such as a cobalt salt,the multilayered packaging article can be used for storingoxygen-sensitive products, such as beer, fruit juice, or the like. Theshelf life of the packaged product widely depends of the amount ofpolyamide in the packaging article and of the thickness of the barrierlayer.

In return, the use of gas barrier polymer, like polyamide in thecontainer wall renders the recycling of the container more difficult. Inaddition, when polyamide is used, in particular for making a monolayercontainer, there is a risk of formation of haze in the container walldue to the orientation of the polyamide during the process for makingthe container. Said haze formation in the container wall is obviouslydetrimental for all the applications where it is important to have atransparent container, —i.e. a container whose wall has no eye-visiblewhitening or haze, in order to have a better appearance of the packagedproduct.

In order to improve the O₂ scavenging performance of a plasticcontainer, it is also known to close the container with a closure capcomprising a layer having O₂ scavenging properties.

Another recent route for making a container having oxygen scavengingproperties is described in PCT application WO 2008/090354. The O₂scavenging properties are obtained by using an active substance, such asfor example a hydride, that is capable of chemically reacting with waterand generating molecular hydrogen, and by making said molecular hydrogenreact with oxygen which may ingress the container. In the variant ofFIG. 4 of s PCT application WO 2008/090354, said active substance isincorporated in a plug that is positioned in a cap. In such a variant,the active substance can however prejudicially contaminate the productstored in the container.

OBJECTIVE OF THE INVENTION

A general and main objective of the invention is to propose a novelclosure cap that includes an active substance capable of chemicallyreacting with water and generating molecular hydrogen into a container.

A more particular objective of the invention is to propose a novelclosure cap, that includes an active substance capable of chemicallyreacting with water and generating molecular hydrogen into a container,and that can be in contact with the content of the container without anyrisk of contamination of the said substance by the active substance.

A more particular objective of the invention is to propose a novelclosure cap, that includes an active substance capable of chemicallyreacting with water and generating molecular hydrogen into a container,and that can be easily manufactured.

A more particular objective of the invention is to propose a novelactive closure cap for a container, said cap being suitable forscavenging oxygen that may penetrate inside the container, notablythrough the permeable wall of the container, or oxygen that is presentin the head space of the container.

SUMMARY OF THE INVENTION

These objectives are achieved by the closure cap of claim 1. Thisclosure cap of the invention comprises a shell that can be fitted onto acontainer for closing an opening of said container, an active layer thatis capable of chemically reacting with water and generating molecularhydrogen, and a liner that is permeable to water vapour and to molecularhydrogen; said active layer has an inner face, an outer face and acircumferential edge; the shell comprises an housing and the activelayer is entirely contained in said housing; the outer face and thecircumferential edge of the active layer are in contact with the shelland are bonded to the shell; the liner is closing said housing and isbonded to the shell on the whole periphery of the active layer and tothe inner face of the active layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear moreclearly on reading the following description of several closure capembodiments, which description is given by way of non-limiting exampleand with reference to the accompanying drawings, in which:

FIG. 1 is a view in cross-section of a first variant of closure capfitted onto a container neck,

FIGS. 2 to 6 are partial views in cross-section of five other variantsof closure cap.

DETAILED DESCRIPTION

In reference to FIG. 1, a closure cap 1 of the invention is fitted ontoa standard neck 2 of a plastic container C comprising a top opening(container mouth), like for example a bottle neck. This top opening ofthe neck 2 is knowingly used for filling the container with a productand/or for pouring the product outside the container. In this particularembodiment, the closure cap 1 is screwed on the container neck 2. Inanother variant, the closure cap 1 could be snapped on the containerneck 2.

The material and the shape of the container are not important. Inparticular the container can be for example any plastic container or anycardboard container; the container can be for example a bottle-shapedcontainer, a flask, a jar, a tube, a bag, a pouch. Within the scope ofthe invention, the container can be rigid, semi rigid or flexible. Thecontainers contemplated in the present invention may be either of amonolayer or a multilayer construction. Suitable materials which may beused as a layer or part of one or more layers in either monolayer ormultilayer containers include polyester (including but not limited toPET), polyetheresters, polyesteramides, polyurethanes, polyimides,polyureas, polyamideimides, polyamides, polyphenyleneoxide, phenoxyresins, epoxy resins, polyolefins (including but not limited topolypropylene and polyethylene), polyacrylates, polystyrene, polyvinyls(including but not limited to polyvinyl chloride)) and combinationsthereof. All of the aforementioned polymers may be in any desiredcombination thereof.

The container C can be manufactured by using any method known in theart, including but not limited to injection moulding, injection blowmoulding (IBM), injection stretch-blow moulding (ISBM), extrusion blowmoulding, thermoforming, rotational moulding, folding.

This closure cap 1 comprises three main components: a closure shell 10,an active layer 11, and a liner 12.

Closure Shell 10

The closure shell 10 is a plastic piece that comprises a top wall 100and a lateral wall 101. The top wall 100 forms a disc and comprises anouter face 100 a and an inner face 100 b that is intended in use to beoriented toward the inside (IN) of the container (FIG. 1). The lateralwall 101 is substantially perpendicular to the top wall and forms asubstantially cylindrical lateral skirt 101. The inner face 101 a ofthis skirt 101 comprises a screwing thread 101 b that can cooperate withthe screwing thread 20 of the neck 2 for securing the closure cap 1 ontothe neck 2.

The closure shell 10 also comprises sealing means for substantiallyhermetically closing the top opening of the container neck 2, andavoiding any leakage of the product contained in the container. In thisparticular example, these sealing means comprise an inner cylindricalsealing lip 102 a and an outer cylindrical sealing lip 102 b, thatextend both from the inner face 100 b of the top wall 100. The outersealing lip 102 b is positioned between the inner sealing lip 102 a andthe skirt 101. These sealing lips 102 a and 102 b can be replaced by anysealing element that cooperates with the container neck for sealing thetop opening of the neck 2, once the closure cap 1 is fitted onto theneck 2.

The inner face 100 b of the top wall 100 comprises a central recess 103that is made in the thickness of the top wall. This recess 103 isdelimited by a bottom wall 103 a and a peripheral lateral wall 103 b.The lateral wall 103 b extends downwardly from the bottom wall 103 a andsurrounds the bottom wall 103 a. This recess 103 forms a housing H forthe active layer 11.

The closure shell 10 further comprises a shoulder portion 104 thatsurrounds the recess 103. Said shoulder portion 104 joins the lateralwall 103 b of the recess 103 to the internal sealing lip 102 a.

The material of the closure shell 10 can be any known thermoplasticmaterial that can be moulded in a mould, and more particularly any knownthermoplastic material that can be processed by injection moulding.Preferably, the closure shell is made from a polyolefin, like forexample polypropylene, polyethylene, polyethylene terephthalate or ablend thereof. A good candidate for making the closure shell 10 is HDPE(High Density Polyethylene).

Active Layer 11

The active layer 11 is for example a disk-shaped layer, with an innerface 11 a, an outer face 11 b, and a circumferential edge 11 c. Theactive layer 11 is positioned inside the recess 103 of the closure shell10 and is entirely contained in the recess 103. More especially, theactive layer 11 completely fills the recess 103 without protrudingoutside the recess 103, the thickness E of the active layer 11 beingsubstantially equal to the depth of the recess 103. The inner face 11 aof the active layer 11 (i.e. face 11 a oriented towards the inside IN ofthe container) is thus flush with the inner face 104 a of the shoulderportion 104, and there is no overlap of the active layer 11 outside therecess 103, and in particular no overlap of the material of the activelayer 11 onto the inner face 104 a of the shoulder portion 104.

The outer face 11 b and the circumferential edge 11 c of the activelayer 11 are in contact with, and are bonded to, respectively the bottomwall 103 a and lateral wall 103 b of the recess 103 of the shell 10. Theactive layer 11 is preferably only thermal bonded to the shell 10, i.e.without using an additional adhesive layer in-between.

The active layer 11 is capable of chemically reacting with water andgenerating molecular hydrogen from this reaction with water. Thematerial of the active layer 11 can be made of or can comprise anyactive substance forming such a hydrogen source. Preferably, but notonly, said active substance suitable for the release of molecularhydrogen as a result of contact with water is one of the activesubstances described in PCT application WO2008/090354.

In one preferred embodiment, the material of the active layer 11comprises a polymeric matrix containing the active substance which isincorporated in the polymer matrix and which is capable of chemicallyreacting with water and generating molecular hydrogen from this reactionwith water.

Suitable polymeric matrix materials include but are not limited to lowdensity polyethylene, in particular linear low density polyethylene,high density polyethylene, polypropylene, ethylene vinyl acetate,thermoplastic elastomers (TPEs), like styrenic block copolymers,polyolefin blends, elastomeric alloys, thermoplasticpolyurethanes,thermoplastic copolyester, and thermoplastic polyamides, or blendthereof. In particular a good candidate among thermoplastic elastomermaterials is a material comprising styrenic block copolymers consistingof polystyrene blocks and rubber blocks, such as for example SEBS, SEPS,SBS, SBC.

The ratio of the weight of active substance to matrix material may be atleast 0.01, preferably at least 0.02. The matrix may be a polymericmatrix and said active substance may be dispersed therein. In general,once an active material is dispersed into a polymer, the rate of releaseof hydrogen is limited by either the permeation rate of water into thepolymeric matrix and/or by the solubility of water in the chosen matrix.Thus, selection of polymeric materials based on the permeability orsolubility of water in the polymer allows one to readily control therate of release of molecular hydrogen from any number of activesubstances.

The polymeric matrix may include at least 1 wt % of active substance,preferably at least 2 wt %. The polymeric matrix may include less than20 wt % of active substance. Suitably, the polymeric matrix includes1-16 wt %, preferably 4-12 wt % of active substance. The balance ofmaterial in the polymeric matrix may predominantly comprise a saidpolymeric material.

Active substances suitable for the release of molecular hydrogen as aresult of contact with water are preferably the ones described in PCTapplication WO2008/090354. In particular, said active substance maycomprise a metal and/or a hydride. Said metal may be selected fromsodium, lithium, potassium, magnesium, zinc or aluminum. A hydride maybe inorganic, for example it may comprise a metal hydride orborohydride; or it may be organic.

More particularly, active substances include but are not limited to:sodium metal, lithium metal, potassium metal, calcium metal, sodiumhydride, lithium hydride, potassium hydride, calcium hydride, magnesiumhydride, sodium borohydride, and lithium borohydride.

Where the rate of reaction between the active substance and water is tooslow, the addition of hydrolysis catalysts and/or agents in thepolymeric matrix can be used. For example, the rate of hydrolysis ofsilicon hydrides may be enhanced by the use of hydroxide or fluorideions, transition metal salts, or noble metal catalysts.

The active substance may also be the polymeric matrix. For example,polymeric silicon hydrides such as poly(methylhydro)siloxane provideboth a polymeric matrix and an active substance capable of releasingmolecular hydrogen when in contact with moisture.

Liner 12

The liner 12 is closing the recess 103 of the shell 10. The liner 12 isin contact with and is bonded to the inner face 11 a of the active layer11 and to the shoulder portion 104 of the shell 10 on the wholeperiphery of the active layer 11.

In this particular variant of FIG. 1, the liner 12 is also in contactwith and is bonded on its whole periphery to the internal sealing lip102 a of the closure shell 10. This characteristic is however notmandatory.

When the closure cap 1 is fitted onto a container C, this liner 12 isfacing the inside IN of the container C, and forms a protective barrierthat prevents the product stored in the container from contacting theactive layer 11 and that prevents the active substance (H₂ generator) ofthe active layer 11 from migrating into the container. This liner 12also to limit the ingress of water in contact with the active layer 11,and thereby enables to obtain a controlled release of molecular hydrogenby the active layer 11 over a prolonged period of time.

Preferably, the liner 12 is only thermal bonded to the active layer 11and to the shell 10, i.e. without using an additional adhesive layer.

The liner 12 can be a monolayer or a multilayer component. The materialof the liner 12 is preferably selected in order to obtain a liner 12that:

-   -   (i) is heat bondable to the closure shell and to the active        layer 11, and    -   (ii) is permeable to water vapour and to molecular hydrogen.

The material of the liner 12 can be any polymeric material that enablesto obtain characteristics (i) and (ii). The materials of the liner 12include but are not limited to low density polyethylene, in particularlinear low density polyethylene, high density polyethylene,polypropylene, ethylene vinyl acetate, thermoplastic elastomers (TPEs),like styrenic block copolymers, polyolefin blends, elastomeric alloys,thermoplasticpolyurethanes, thermoplastic copolyester, and thermoplasticpolyamides, or blend thereof. In particular a good candidate amongthermoplastic elastomer materials is a material comprising styrenicblock copolymers consisting of polystyrene blocks and rubber blocks,such as for example SEBS, SEPS, SBS, SBC.

Bonding of the Liner 12 with the Closure Shell 10

An efficient bonding between the liner 12 and the closure shell 10 isvery important, in order to avoid delamination problems that woulddetrimentally lead to a risk of leakage and contact of the active layer11 with the product stored in the container, and thereby to a risk ofcontamination of the product.

This efficient bonding is preferably obtained by using materials for theclosure shell 10 and the liner 12 that are compatible in terms ofthermal bonding, and that enable to achieve a very good thermal bondingof the liner 12 with the shell 10. To this end, the material of theliner 12 and the material of the closure shell 10 comprise, or are madeof, at least one identical polymer. The material of the liner 12 canhowever be a polymeric material that differs from the material of theclosure shell 10. In a preferred embodiment, the closure shell 10 wasfor example in HDPE and the liner 12 was a monolayer liner made of EVAor LLDPE or a thermoplastic elastomer comprising polyolefin blends orSEBS blends.

This efficient bonding is also improved by the particular structure ofthe closure cap with a recess 103 containing the active layer 11 andwith a shoulder peripheral bonding portion 104. Thanks to the recess103, the active layer 11 does not exert onto the liner 12 a mechanicalaction that would contribute to delaminate the liner 12 from the closureshell 10. The width (I) of the shoulder bonding portion 104 (FIG. 1)will be selected by one skilled in the art in order to obtain asufficient bonding area between the liner 12 and the shell 10, and toavoid any risk of delamination during normal use.

FIGS. 2 to 6 show other variants for the closure cap.

In the variant of FIG. 3, the top wall 100 of the shell 10 comprises arecess 103, but in contrast with the variant of FIGS. 1, 2, 4, 5 and 6,does not comprise a shoulder bonding portion 104 for bonding the liner12 to the shell 10. In this variant, the liner 12 is bonded to the shellonly on its circumferential edge 12 a.

When the liner 12 is in contact with the internal sealing lip 102 a(like for example in the variants of FIGS. 1 and 2), there is a riskthat the liner 12 exerts a mechanical constraint on the lips that leadsto a deformation of the lip 102 a. Such a deformation can provokeleakage problems when the cap is fitted onto a container. To avoid thisproblem, in the variants of FIGS. 4 to 6, the liner 12 is advantageouslynot in contact with the internal sealing lip 102 a, and there is a gap Gbetween the circumferential edge 12 a of the liner 12 and the internalsealing lip 102 a.

Manufacturing Process

The closure 1 can be for easily and quickly manufactured by using anover injection technique.

In a first step, the closure shell 10 is injection moulded in a mould.In a second step, the active layer 11 is over injected onto the closureshell. Then in a third step, the liner 12 is over injected onto theclosure shell 10 and active layer 11.

During injection, the active layer 11 is compressed in the injectionmould. When this mould is opened, a decompression of the active layer 11can occur. In such a case the active layer 11 exerts on the liner 12 apressure that pushes the liner 12 away from the shell 10. The bonding ofthe liner 12 is thus less strong, which can lead to detrimentaldelamination problems. To solve this problem, especially (but not only)when the active layer 11 comprises a thermoplastic elastomer, it ispreferable that the hardness of the active layer 11, for examplemeasured with a durometer according to ASTM D2240, is not less thanShore A hardness 40.

O₂ Scavenging

In use, when the container C is containing a product, in particular anoxygen-sensitive product, and is closed by the closure cap 1, the liner12 avoids any contact between the active layer 11 and the product storedin the container C. The water vapour contained in the head space ofcontainer penetrates through the liner 12 and enters in contact with theactive layer 11.

As a result, the active substance of the active layer 11 producesmolecular hydrogen that migrates through the liner 12 and penetrates inthe container head space. This molecular hydrogen combines with oxygenwhich may have entered in the container through its permeable wall. As aresult a reaction between hydrogen and oxygen takes place, and water isproduced. This oxygen scavenging reaction can be catalysed by a catalystincorporated in the closure cap 1 and/or in the container wall and/or inthe container neck.

A large number of catalysts are known to catalyze the reaction ofhydrogen with oxygen, including many transition metals, metal borides(such as nickel boride), metal carbides (such as titanium carbide),metal nitrides (such as titanium nitride), and transition metal saltsand complexes. Group VIII metals are particularly efficacious. Of theGroup VIII metals, palladium and platinum are especially preferredbecause of their low toxicity and extreme efficiency in catalyzing theconversion of hydrogen and oxygen to water with little or no byproductformation. The catalyst is preferably a redox catalyst.

Preferably, but not necessarily, for facilitating the recycling of theclosure 1, the closure cap 1 has a density less than 1, and the closureshell 10, the active layer 11, and the liner 12, have respectively threedifferent colours in order to visually differentiate them. This isobtained for example by adding a first colorant (for example red) to thepolymeric material of the active layer 11, and by adding a differentcolorant (for example blue) to the polymeric material of the liner 12,the shell 10 containing for example no colorant and being substantiallywhite. The addition of colorant can be performed prior to injection orduring the injection of closure cap components. In a variant, a thirdcolorant (for example green) can be also added to the polymeric materialof the shell 10.

1. A closure cap (1) comprising a shell (10) that can be fitted onto acontainer for closing an opening of said container, an active layer (11)that is capable of chemically reacting with water and generatingmolecular hydrogen, and a liner (12) that is permeable to water vapourand to molecular hydrogen, wherein said active layer (11) has an innerface (11 a), an outer face (11 b) and a circumferential edge (11 c),wherein the shell (10) comprises an housing (H) and the active layer(11) is entirely contained in said housing (H), wherein the outer face(11 b) and the circumferential edge (11 c) of the active layer (11) arein contact with the shell (10) and are bonded to the shell (10), andwherein the liner (12) is closing said housing (H) and is bonded to theshell (10) on the whole periphery of the active layer (11) and to theinner face (11 a) of the active layer (11).
 2. The closure of claim 1,wherein the shell (10) comprises a top wall (100) having a recess (103)that forms the said housing (H), and wherein the liner (12) is closingthe said recess (103) and is bonded to the shell (10) on the wholeperiphery of the said recess (103).
 3. The closure of claim 1, whereinthe shell (10) comprises a shoulder portion (104) that surrounds therecess (103), and the liner (12) is bonded to the shoulder portion (104)on the whole periphery of the recess (103).
 4. The closure of claim 3,wherein the active layer (11) is flush with said shoulder portion (104).5. The closure of claim 2, wherein the active layer (11) completelyfills the recess (103) without protruding outside the recess (103). 6.The closure of claim 1, wherein the shell (10) comprises an innercylindrical sealing lip (102 a) and wherein the liner (12) is not incontact with the inner cylindrical sealing lip (102 a).
 7. The closureof claim 1, wherein the active layer (11) and the liner (12) are overinjected onto a moulded shell (10).
 8. The closure of claim 1, whereinthe active layer (11) comprises an active substance that is capable ofchemically reacting with water and generating molecular hydrogen.
 9. Theclosure of claim 8, wherein the active substance is selected from thegroup comprising Group I, II, and III metals, Group I, II, and III metalhydrides, rare earth metals, rare earth hydrides, alkali metalborohydrides, alkaline earth metal borohydrides, alkali metal aluminumhydrides, silicon hydrides, tin hydrides, and combinations thereof. 10.The closure of claim 8, wherein the active substance is selected fromthe group comprising sodium hydride, lithium hydride, sodiumborohydride, sodium metal, lithium metal, potassium metal, calciumhydride, magnesium hydride, lithium aluminum hydride, and combinationsthereof.
 11. The closure of claim 1, wherein the active layer (11)comprises a polymeric matrix.
 12. The closure of claim 11, wherein thepolymeric matrix comprises a polyethylene.
 13. The closure of claim 11,wherein the polymeric matrix comprises an ethylene vinyl acetatecopolymer.
 14. The closure of claim 11, wherein the polymeric matrixcomprises a thermoplastic elastomer.
 15. The closure of claim 14,wherein the thermoplastic elastomer comprises a polyolefin blend. 16.The closure of claim 14, wherein the thermoplastic elastomer comprisesSEBS.
 17. The closure of claim 1, wherein the hardness of the activelayer (11) is not less than Shore A hardness
 40. 18. The closure ofclaim 1, wherein the liner (12) comprises a polyethylene.
 19. Theclosure of claim 1, wherein the liner (12) comprises a thermoplasticelastomer.
 20. The closure of claim 19, wherein the thermoplasticelastomer comprises a polyolefin blend.
 21. The closure of claim 19,wherein the thermoplastic elastomer comprises SEBS.
 22. The closure ofclaim 1, wherein the liner (12) comprises an ethylene vinyl acetatecopolymer.
 23. The closure of claim 1, wherein the shell (10) is made ofa polymeric material comprising a polyolefin.
 24. The closure of claim1, wherein the material of the liner (12) and the material of theclosure shell (10) comprise, or are made of, at least one identicalpolymer.
 25. The closure of claim 1, wherein the liner (12) is onlythermal bonded to the closure shell (10) and to the active layer (11).26. The closure of claim 1, wherein the shell (10), the active layer(11), and the liner (12) have respectively three different colours inorder to visually differentiate them.
 27. The closure of claim 1, havinga density less than
 1. 28. An assembly comprising a plastic containerand a closure cap, wherein the closure cap (1) is defined by claim 1.29. The assembly of claim 28, wherein the plastic container and/or theclosure cap (1) comprises a catalyst for promoting a reaction betweenmolecular hydrogen and molecular oxygen.